The present invention relates to data communication switching, and more particularly to local area network (LAN) switching.
LAN switches interconnect network devices residing on different protocol domains. The switching functionality provided by LAN switches typically includes “local” switching between network devices on protocol domains interfacing with the same switching controller and “backplane” switching between network devices on protocol domains interfacing with different switching controllers. The backplanes used in LAN switch backplane switching have generally been configured as a packet bus shared by a plurality of controllers. A conventional LAN switch backplane is illustrated in FIG. 1. LAN switch backplane 10 includes switching controllers 110, 120, 130 and a management controller 140 taking turns transmitting packets over packet bus 150 and asserting a shared claim line 160 to notify other controllers when they have captured a packet off bus 150. Management controller 140 is the “nerve center” of the backplane which assists switching controllers 110, 120, 130 in learning information for use in determining whether packets are to be captured or filtered and communicates such information to switching controllers 110, 120, 130 on management bus 170. In such conventional backplanes, orderly transmission over the packet bus is known to have been accomplished in several ways. One way is assigning the controllers different time slots in a repetitive timing cycle and granting control of the packet bus to the controllers round-robin in accordance with their assigned time slots. Another way involves conducting a priority-based arbitration among the controllers having packets for transmission and granting control of the bus to the controller which wins the arbitration. Regardless of whether one of these or some other ordering scheme is implemented, reliance on a shared bandwidth backplane, and its inherent requirement of regulating access in order to guarantee contention-free transmission, has led to congestion at the transmit side of such backplanes and inefficient use of resources at the receive side of such backplanes. For example, packets transmitted across the packet bus often captured off the bus by only one switching controller and are filtered by others. However, due to its essential broadcast nature, all controllers must wait for the packet to clear the packet bus before the next packet can be transmitted. This delay results in clock cycles in which the receive resources of many controllers are idle, even while congestion may be developing at the transmit side. Thus, a more efficient LAN switch backplane is needed, particularly as network devices relying on such backplanes continue to migrate to ever-higher transmission rate protocols.